الفهرس 
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Abstract
Sheep milk is an excellent raw material for the milk processing industry especially in cheese production. The protein content and composition of sheep milk are important in the cheese manufacturing and considered a major factor in determination of the quality for yield and the final product.
In Egypt; sheep is raised for meat and wool only except coastal regions and oases. The aim of this thesis is to identify the genetic polymorphism of six ovine milk protein genes in Egyptian sheep as a tool for genetic improvement of milk trait characteristics in Egyptian sheep.
Blood samples were collected from eighty-seven animals belonging to three main breeds of Egyptian sheep; Rahmani, Barki and Ossimi. Genomic DNA was extracted from the whole blood by salting-out method and prepared for PCR application. The specific primers were designed for six genes; two major whey protein genes, α-lactalbumin (α-LA) and β-lactoglobulin (β-LG), and four casein protein genes, αS1-casein (αS1-CN), αS2-casein (αs2-CN), β-casein (β-CN) and κ-casein (κ-CN). Two techniques were used in this study; PCR-RFLP and PCR-SSCP.
The PCR amplified fragment of α-LA exon 1 was at 166-bp in size. The SSCP results showed two different patterns resulted from two nucleotides substitution in non-coding region; GC in pattern I are substituted with CT in pattern II. The frequencies were 92.86% and 7.14% in Rahmani, 89.66% and 10.34% in Ossimi and 81.48% and 18.52% in Barki, respectively.
PCR amplified fragments of β-LG (452-bp) were digested by restriction enzyme RsaI. The result showed the presence of three genotypes; AA, AB and BB in the tested breeds. The genotype frequencies were 90%, 10%, 0% in Rahmani; 68.97%, 3.45%, 27.59% in Ossimi and 48.15%, 7.41%, 44.44% in Barki, respectively.
A 223-bp fragment of αS1-CN gene was amplified by PCR. SSCP result recorded the presence of three different patterns; TT, TC and CC; in eighty-seven tested sheep animals. The sequence analysis of two homologous patterns showed a single nucleotide polymorphism (SNP) (T→C) at position 170. The frequencies of three patterns in the tested sheep breeds were 43.33%, 50.00%, 6.67% in Rahmani; 83.33%, 13.33%, 3.33% in Ossimi and 74.07%, 22.22%, 3.70% in Barki, respectively.
The restriction digestion of αs2-CN PCR product (1300-bp) by Tru1I endonuclease revealed three different genotypes; AA, AG and GG with frequencies 66.67%, 30.00%, 3.33% in Rahmani; 96.67%, 3.33%, 0% in Ossimi and 96.15%, 3.85%, 0% in Barki, respectively. The sequence analysis revealed the presence of a single nucleotide polymorphism (A→G) in intron 6 which leads to an additional restriction site for allele A.
The SSCP of β-CN exon 7 revealed two different patterns and the sequence analysis of the PCR product (299-bp) of these patterns showed two single nucleotide substitutions; AC and C T without any amino acid exchange. The frequencies of these two different patterns were 96.67% and 3.33% in Rahmani; 65.52% and 34.48% in Ossimi and 88.46% and 11.54% in Barki, respectively.
The polymorphism of κ-casein gene was detected in this study using PCR-SSCP technique. PCR amplified a fragment with 406-bp in exon 4. SSCP result of κ-Casein gene showed that all tested sheep animals are monomorphic. The alignment between our sequences with published sequence revealed two nucleotide substitutions; CT and TC.